NON-CONTACT MECHANICAL ENERGY HARVESTING DEVICE AND METHOD UTILIZING FREQUENCY RECTIFICATION
An energy harvesting apparatus includes an inverse frequency rectifier structured to receive mechanical energy at a first frequency, and a solid state electromechanical transducer coupled to the inverse frequency rectifier to receive a force provided by the inverse frequency rectifier. The force, when provided by the inverse frequency rectifier, causes the solid state transducer to be subjected to a second frequency that is higher than the first frequency to thereby generate electrical power. The coupling of the solid state electromechanical transducer to the inverse frequency rectifier is a non-contact coupling.
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This application claims priority to U.S. Provisional Application No. 60/876,526 filed Dec. 22, 2006 and to U.S. Provisional Application No. 60/881,152 filed Jan. 19, 2006, the entire contents of which are hereby incorporated by reference.
BACKGROUND1. Field of Invention
The present invention relates to energy harvesting, and more particularly to non-contact mechanical energy harvesting utilizing frequency rectification.
2. Discussion of Related Art
Energy harvesting (or energy scavenging) is defined as the conversion of ambient mechanical energy, for example, but not limited to, vibrational energy, into usable electrical energy. The electrical energy harvested can then be used as a power source for a variety of low-power applications, such as, but not limited to, remote applications that may involve networked systems of wireless sensors and/or communication nodes, where other power sources such as batteries may be impractical [J. A. Paradiso, T. Starner, IEEE Pervasive Computing, January-March:18-27 (2005); S. Roundy, E. S. Leland, J. Baker, E. Carleton, E. Reilly, E. Lai, B. Otis, J. M. Rabacy, P. K. Wright, IEEE Pervasive Computing, January-March:28-35 (2005)]. For these reasons, the amount of research devoted to power harvesting has been rapidly increasing [H. A. Sodano, D. J. Inman, G. Park, The Shook and Vibration Digest, Vol. 36: 197-205 (2004)].
[Vibration-based energy harvesters have been successfully developed using, for example, electromagnetic, electrostatic, and piezoelectric methods of electromechanical generation [S. Roundy, E. S. Leland, J. Baker, E. Carleton, E. Reilly, E. Lai, B. Otis, J. M. Rabacy, P. K. Wright, IEEE Pervasive Computing, January-March: 28-35 (2005)]. A piezoelectric harvester has gained considerable attention because piezoelectric energy conversion produces relatively higher voltage than other electromechanical generators. A piezoelectric harvester can convert mechanical energy into electrical energy by straining a piezoelectric material that then uses atomic deformations to change the polarization of the material and to produce net voltage changes. The net voltage can be scavenged and converted into stored power in either a battery or a capacitor, or it may be used as it is being created.
The amount of power accumulated via the piezoelectric harvester (or generator) is proportional to the mechanical frequency which is exciting it [H. W. Kim, A. Batra, S. Priya, K. Uchino, D. Markley, R. E. Newnham, H. F. Hofmann, The Japan Society of Applied Physics, Vol. 43 9A:6178-6183 (2004)]. In most non-resonant energy generators, the mechanical frequency input to the generator (e.g., piezoelectric material) corresponds to the environment's dominant mechanical frequency, which in most all cases is relatively low (i.e., below 100 Hz). For example, a heel-strike power harvester [N. S. Shenck, J. A. Paradiso, IEEE Micro, Vol. 21:30-41 (2001)], disclosed in U.S. Pat. No. 6,433,465 B1 (Mcknight et al.), harvests energy from a walking motion that occurs at approximately 1 Hz. The frequency of this generator matches the driving frequency of the heel strike. This low frequency generator limits the amount of electromechanical power that can be converted in a give volume. As a result, the power harvested via the non-resonant generator is insufficient to power most electronic-based systems. Therefore, a relatively small non-resonant generator may, typically, not be able to generate sufficient power due to the low-frequency ambient vibrations.
On the other hand, a resonant piezoelectric generator is disclosed in U.S. Pat. No. 3,456,134 (Ko et al.), U.S. Pat. No. 4,900,970 (Ando et al.) and U.S. Pat. No. 6,858,870 B2 (Malkin et al.). For the resonant vibration-based generators, the harvesting power can be maximized when the resonance frequency matches the driving frequency of the ambient vibration source [J. A. Paradiso, T. Starner, IEEE Pervasive Computing, January-March:18-27 (2005)]. Otherwise, the harvesting power output drops off dramatically as resonance frequency deviates from the driving frequency. To harvest maximum energy, the piezoelectric generator in such systems is designed to exploit the oscillation of a proof mass resonantly tuned to the environment's dominant mechanical frequency [S. Roundy, E. S. Leland, J. Baker, E. Carleton, E. Reilly, E. Laf, B. Otis, J. M. Rabacy, P. K. Wright, IEEE Pervasive Computing, January-March:28-35 (2005)]. The resonance frequency based harvesting approach limits operation to a very narrow frequency band and does not utilize the higher frequencies available from piezoelectric materials.
Conventional mechanical energy harvesting devices for micro-system use can be categorized into four different vibration-based mechanisms, as follows:
1. Piezoelectric based systems in which input vibrations are converted one-to-one for output power. These are based on the piezoelectric cantilever beam and proof mass arrangement such as illustrated in
2. Electrostatic based systems in which input vibrations are converted one-to-one for output power. These are based on the change of capacitance in the gap caused by relative motion of structures such as illustrated in
3. Electro-magnetic based systems in which input vibrations are converted one-to-one for output power. These are based on magnet and coil arrangements such as illustrated in
4. Acoustic based systems in which input acoustic waves are converted one-to-one for output power. These are based on the acoustic wave and related mechanical structure such as illustrated in
Because most structural resonance frequencies are small (i.e., below 100 Hz), the amount of power that can be harvested per unit volume per device is limited because power is proportional to input frequency. It is therefore desirable to convert a low-range mechanical frequency to a higher resonant frequency, given that many conversion based systems such as piezoelectric materials and magnetostrictive materials are capable of operating at frequencies in the 10's of kHz. Harvesting power at these elevated frequencies represent orders of magnitude increases in power harvested per unit volume of device. In addition, mechanical energy harvesting devices that have moving parts that come in contact with each other result in decreased useful lifetimes and reliability problems. Therefore, there exists a need for improved mechanical energy harvesting devices and methods.
SUMMARYAn energy harvesting apparatus according to an embodiment of the invention includes an inverse frequency rectifier structured to receive mechanical energy at a first frequency, and a solid state electromechanical transducer coupled to the inverse frequency rectifier to receive a force provided by the inverse frequency rectifier. The force, when provided by the inverse frequency rectifier, causes the solid state transducer to be subjected to a second frequency that is higher than the first frequency to thereby generate electrical power. The coupling of the solid state electromechanical transducer to the inverse frequency rectifier is via non-contact coupling. A system according to embodiments of the invention may comprise the above-described apparatus, as well as an electrical device coupled to receive the electrical signal. Embodiments of the invention may also include methods of implementing the above-described apparatus. Embodiments of the current invention may also include methods of manufacturing apparatuses according to the current invention.
The rectified frequency may be applied to an electro-mechanical or magneto-mechanical material to convert the mechanical power into electrical power. By using an electro-mechanical material a voltage-based harvesting system may be obtained, while by using a magneto-mechanical material a current-based harvesting system may be obtained.
Additional features of this invention are provided in the following detailed description of various embodiments of the invention with reference to the drawings. Furthermore, the above-discussed and other attendant advantages of the present invention will become better understood by reference to the detailed description when taken in conjunction with the accompanying drawings, in which:
The present invention represents a significant advancement compared to prior energy harvesting designs. An inverse frequency rectification device and method according to embodiments of the current invention converts a low frequency oscillation source, which may, for example, be from an ambient vibration, to a much higher frequency oscillation. This rectification allows substantially more power per unit mass to be harvested than previously possible. To date all the energy harvesters have relied on the relatively low ambient vibrations and have not used inverse frequency rectification. The addition of frequency rectifiers can dramatically increase the power output per unit volume. The inverse frequency rectification approach can potentially generate power densities on the order of W/cm3 levels, two to three orders of magnitude larger than currently obtainable by conventional piezoelectric energy harvesters.
Inverse frequency rectification may be provided in accordance with embodiments of the present invention to generate higher resonant frequency vibration without changing the generator design for resonance-tuning. Given this, it may be advantageous to have a single design that operates effectively over a range of vibration frequencies. The following detailed description sets forth examples of embodiments of the current invention to facilitate an explanation of concepts of this invention. The current invention is not limited to the specific embodiments described in detail.
As discussed above, the above embodiments are shown in the figures using an inverse frequency rectification scheme in which a bar or other surface having transversely mounted tooth-like rectifiers is vibrated such that the rectifiers cause a flexible, displaceable structure to repeatedly be excited into vibration. However, the invention is not intended to be limited to such embodiments. Rather the invention is intended to encompass any inverse frequency rectification method or device in accordance with the general concepts of this invention, including circular, linear, or otherwise approaches. For example, an alternative structure may use gears to achieve inverse frequency rectification in a circular fashion. Another alternative structure may utilize a rack-and-pinion-based system to achieve a continuous non-discrete system.
A system like that of
The following is an example of fabricating methods for a developing a non-contact frequency rectification system. Two main structural components of such an embodiment, i.e., (1) a non-contact array (e.g. NdFeB Magnetic Array) and (2) a solid state electro-mechanical converter, maybe fabricated according to an embodiment of the current invention as described below. However, methods of manufacture according to the current invention are not limited to this example and include scales from nano to macro (cm). After fabrication, the components (1) & (2) may be assembled using various related techniques including MEMS (deposit sacrificial layer, deposit binding film, etch to specific pattern) or alternatively the entire system may be fabricated simultaneously on a single wafer. Below we describe the fabrication details of an example that has a NdFeB magnetic array and a piezoelectric electromechanical energy converter. The current invention is not limited to only this example. The example focuses on the manufacturing process to create the magnetic array. This is the primary focus because the spacing of the magnets will typically translate in the degree of rectification. Also while the description is in terms of NdFeB, other magnetic materials could also be used as well as other fabrication procedures.
(1) NdFeB Magnetic Array Fabrication Process
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- Macro-Scale Fabrication Process
For a macroscopic system the Nd—Fe—B is melt spun onto a surface. Following the deposition of the Nd—Fe—B onto the surface, the Nd—Fe—B is mechanically machined into isolated regions. A representative dimension between magnets can be down to 100 microns in spacing. Once the system is geometrically in place, the Nd—Fe—B system is magnetized with a strong magnetic field at elevated temperature.
-
- Micro-Scale Fabrication Process
For microscale fabrication the NdFeB is typically sputter deposited onto a silicon wafer. Once deposited, a photoresist is spin coated on the surface and patterned into the desired dimensions. A typically dimension can be down to 1 micron in spacing. Following the patterning of the photoresist, the NdFeB is etched with a Salpetric Acid solution to form the structure of the magnetic rectificater. Following fabrication the system is magnetically poled at an elevated temperature.
-
- Nano-Scale Fabrication Process (Shown as
FIG. 14 )
- Nano-Scale Fabrication Process (Shown as
For nanoscale fabrication a nano-imprinting lithographic approach is used. Nanoimprint lithography creates a resist relief pattern by deforming the resist physical shape with embossing. Nanoimprint lithography can produce sub-10 nm features over a large area with low cost. In the imprinting process, a mold with nanostructures on its surface is pressed into a thin resist cast on a substrate. The resist, a thermal plastic, for example, but not limited to polymethylmethacrylate (PMMA), is deformed readily by the mold when heated above its glass transition temperature. After the resist is cooled below its glass transition temperature, the mold is removed. Following the mold removal, an anisotropic etching process such as reactive ion etching is used to remove the residual resist in the compressed area. Following the imprinting process, the NdFeB system is sputter deposited onto the surface as shown in
The breadboard system in the example illustrated in
A fabrication process for the energy harvesting apparatus in the embodiment of
The specific embodiments described above show magnet arrays that have discrete magnets. However, the current invention is not limited to only those particular examples. For example in other embodiments of the current invention, a substantially continuous layer of magnetic material could have a pattern of magnetic polarities that vary in orientation across the surface somewhat similar to how magnetic polarities vary across the surface of a magnetic recording medium, such as a computer hard drive.
The invention has been described in detail with respect to various embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the claims is intended to cover all such changes and modifications as fall within the true spirit of the invention.
Claims
1. An energy harvesting apparatus, comprising:
- an inverse frequency rectifier structured to receive mechanical energy at a first frequency; and
- a solid state electromechanical transducer coupled to said inverse frequency rectifier to receive a force provided by said inverse frequency rectifier,
- wherein said force when provided by said inverse frequency rectifier causes said solid state transducer to be subjected to a second frequency that is higher than said first frequency to thereby generate electrical power, and
- wherein said coupling of said solid state electromechanical transducer to said inverse frequency rectifier is a non-contact coupling.
2. The apparatus according to claim 1, wherein said coupling of said solid state electromechanical transducer to said inverse frequency rectifier is by at least one of magnetic, Coulomb and Van der Waals forces.
3. The apparatus according to claim 1, wherein said solid state electromechanical transducer comprises a piezoelectric material.
4. The apparatus according to claim 3, wherein said solid state electromechanical transducer comprises a magnet attached to said piezoelectric material.
5. The apparatus according to claim 1, wherein said inverse frequency rectifier comprises an array of magnets.
6. The apparatus according to claim 4, wherein said inverse frequency rectifier comprises an array of magnets.
7. The apparatus according to claim 5, wherein said array of magnets alternates in polarity.
8. The apparatus according to claim 6, wherein said array of magnets alternates in polarity.
9. The apparatus according to claim 1, wherein said energy harvesting apparatus is a micro electromechanical system.
10. The apparatus according to claim 1, wherein said solid state electromechanical transducer comprises at least one of an electrostrictive, a magnetostrictive, a ferroelectric and a ferromagnetic material.
11. The apparatus according to claim 1, further comprising:
- an electrical storage device coupled to receive said electrical power.
12. The apparatus according to claim 11, wherein said electrical storage device comprises a battery.
13. The apparatus according to claim 11, wherein said electrical storage device comprises a capacitor.
14. An electrical system, comprising:
- an energy harvesting apparatus, comprising: an inverse frequency rectifier structured to receive mechanical energy at a first frequency; and a solid state electromechanical transducer coupled to said inverse frequency rectifier to receive a force provided by said inverse frequency rectifier, wherein said force when provided by said inverse frequency rectifier causes said solid state transducer to be subjected to a second frequency that is higher than said first frequency to thereby generate electrical power, and wherein said coupling of said solid state electromechanical transducer to said inverse frequency rectifier is a non-contact coupling; and
- an electrical device coupled to receive said electrical power generated by said energy harvesting apparatus.
15. The system according to claim 14, wherein said electrical device comprises a sensor.
16. The system according to claim 14, wherein said electrical device comprises a communication device.
17. A method of harvesting electrical energy from an environment, comprising:
- providing a mechanical structure adapted to be excited into a periodic motion at a first frequency upon being exposed to said environment; and
- non-contact coupling said mechanical structure to a solid state component to cause said solid state component to be excited into a periodic motion by a second frequency that is higher than said first frequency,
- wherein said solid state component is suitable to generate electrical power at said second frequency when excited through said non-contact coupling to said mechanical structure.
18. The method according to claim 17, further comprising:
- storing electrical energy produced by said solid state component.
19. The method according to claim 17, further comprising:
- powering an electrical device with electrical energy produced by said solid state component.
20. A method of producing an energy harvesting apparatus, comprising:
- forming a frame;
- forming a glider that is in vibrational attachment to said frame, said glider comprising an array of magnets; and
- forming a magnetic probe attached to said frame and arranged proximate said glider such that said glider and said magnetic probe have a space reserved therebetween,
- wherein said glider and said magnetic probe remain free of contact with each other while said energy harvesting apparatus is in operation.
Type: Application
Filed: Dec 21, 2007
Publication Date: Oct 25, 2012
Applicant: The Regents of the University of California (Oakland, CA)
Inventors: Gregory P. Carman (Los Angeles, CA), Dong Gun Lee (Los Angeles, CA)
Application Number: 12/518,613
International Classification: H01L 41/113 (20060101);